If you want to write in a straight line using gimp can you drag a line from the top down to where you want the copied and pasted letters to go? So the word appears completely straight? Is the text recognize function which can recognize the font and then you just type it?
Why aren't you using the text tool? You can write more than 1 letter at a time, and so long as you maintain a file format which supports it, you can even go back and edit the text after saving it.